I've pretty much codified, in my mind, the steps to being unfriended by me.
First, there are sudden death unfriendings. They include if I learn that you have lied to me, or involved me in your lies without my knowledge. (If you're getting a kitten for your child and you want it to stay at my house until the gifting, I'll be happy to participate. But, if you're cheating on your spouse, forget it.) Also, if you post seriously offensive stuff. I'm not really talking about differences of opinion. I'm thinking more in line with the former friend who, upon learning that her pet boy had cheated on her, posted several posts that were increasingly violent towards the young man and his other love. The post that go her "sudden death" was when she combined overt racism with a violent threat. Buh-bye.
But, for the rest of folks, if you post stuff I find offensive or in poor taste, first, I will hide the post. If you post something that I believe is hurtful to others, I might send you a private message expressing my concern. Your response could put you in the running for being unfriended. If you post enough things I feel the need to hide, I will remove you from my feed. This seems to be the easiest way to not interfere with anyone's first amendment rights while also removing the temptation to snark.
If, after I have removed you from my feed, you go out of your way to be an ass, I'm done with you.
In the aftermath of the horrific shooting yesterday, one of my "friends" posted that "guns don't kill people, people kill people." I hid it from my feed. That's strike one.